I mostly shoot landscapes and I find about 80-90% are taken with my 24-105 (I'm on Canon full frame). I have owned two ultra wide lenses, a 16-35 and a 17-35. But currently 24mm is the widest I have. I find that I don't often miss having anything wider than 24mm, except for the odd occasion wanting to shoot in a tight space where you are close to something (eg in a narrow valley trying to shoot a waterfall).
The 24-105 is wide enough to get most landscape shots and gives enough zoom to get in fairly close. If you want a wider shot, you can just shoot a panorama and stitch it later.
It also depends on the landscape. I shoot mostly in East Anglia and find that a wide lens just makes a fairly flat landscape look even flatter. If you use a longer focal length it adds more depth and doesn't show the flatness so much.
As for the filter question, grads are useful but it depends on your preference. Some people get on with them, some dislike the faff.
Bracketing and exposure blending can be fine and works well if you are always using a tripod, but I'm not always on a tripod. It also doesn't work so well for all scenes.
It's a personal choice and the only way to work it out is to try the different methods yourself. Try bracketing and blending as that isn't going to cost you any money. Then also try some filters. You can pick up second hand filters from the classifieds here or from MPB/WEX, Lee filters are decent quality and can be found secondhand for reasonable money.
All the methods are there for you to use, try all the tools, mix and match, see what works for you.